Ionizing radiation detector of the scintillation photoconductive type



Aug. 20, 1963 J. w. TAYLOR 3,101,403

IONIZING RADIATION DETECTOR OF THE SCINTILLATION PHOTOCONDUCTIVE TYPE Filed Jan. 18, 1961 A.C. SUPPLY SCINTILLATOR PHOTOCONDUCTOR INDICATOR ELECTROLUMINESCENT MATERIAL QUENCHER INVENTOR.

JOHN w. TAYLOR ATTORNEY Uni St ws IONIZING RADIATION DETECTOR OF THE SCIN- TELATION PHOTOCONDUCTIVE TYPE John W. Taylor, Philadelphia; Pa; assignor to theUnit'ed represented by the Secretary-got the Navy J 2 States of America. as

Filed Jan. 18,1961, set. No. 83,59 6

6 Claims. e1. 250 -715 (Granted under Title 35, US. Code (1952 Sam) .The invention describedherein may be manufactured It is another object of the invention to. provide an int pact, convenient and practical.

time Patented Aug..20 1963 proved device for gdetectingan'd indicating ionizing radia-' tion which will be relatively inexpensive, simple, com- Various otherobjects and advantages willappear from the following'description of one embodiment of the in- I yention, and the most novelfeatures will be particularly 1 claims. I 7

and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor. ,I, z

The present invention relates to apparatus for detect- 'ing'and indicating ionizing radiation and more particularly to a direct-readingdevice responsive to ionizing radiationland adaptablexfor either personnel or area monitoring.

The presence of radiant energyiin both nailit'aryand pointedoutlher inafter in connectionwith the appended The, accompanying drawing diagrammatically representsanfionizing radiation detecting d indicating device .of thespresent invention. a s l 1 In thejillustrated embodiment of the invention, a detecting head indicated generally by the. numeral 10, an

alternating-current electrical supply .11, an indicator 12,

and a quencher =13 are connected in seriestoforma closed I circuit. The order of their connection is not restricted industrial'environments has (become increasingly. more common in certain technological activities. Conversely, the numberof persons engaged insuoh activities has also multiplied. Although ionization occurring from radiant energy produces biological eifects of diagnostic and theraare also injurious. The invisible ionizing radiation penetratingthe body-of a person causes, no painyet without warning can cause severe injury. Thereforepthequantity of ionizing radiation mustbe measured to warn the to the particular embodiment illustrated. v

The'gdetecting head 10 has its electrical terminals connected to'; two electrically conductive opaque plates .14

which are maintained separated from and in fixed relatiCI1 ,tO- each other by a combination of three distinct 1 materials which may be formed as adjacent'layers, as a .25 peutic value, exposures above-prescribed tolerance levels person when conditions of radioactivity exceed a certain a struction for better accuracy and reliability such as portable and mounted ionization.chamber-type I scintillatiomtypedetectors. *Itis thus notable that. there were no personnel ionizing radiation detector-s hereto- .fore available which embodies the accuracy and reliability of the area monitoring type at a relatively low cost.

- Even if. cost and size were of no moment, the convenhomogeneous mixture, or in any other convenient manner; .F or convenience of illustration'the three materials aresho wn in: distinct "layers. 7 I sciutillationmaterial 16, a photoconductive material 17,

and a electroluminescent materiality The photocon ductivematerial 17 is. a composition, such as cadmium sulphide (CdS), or a, mixture which can produce a" large change. in impedance with only a slight change in light intensity at a given wavelength. The wavelength, ,however," should be prescribed in the spectral regions in which the scintillation material 16 and electroluminescent material ISgenenate maximum light emission.

The'scintillatio'n material 16 is of a composition, such as activated zinc sulphide (ZnS), or a mixture which can convert ionizing radiation into light frequencies in the tional ionizing radiation detectors re main unsuitable in certain environments such as strong-magnetic and radio frequency cfields,-such' as geneuatedin radar apparatus where there is also ionizing 'X-nadiation. For instance, the conventional 'scintillatiomtype detector has its emission to a first dynode of a photo -multiplier and requires .-a stabilized high. voltage direct current-supply, and iisf.

commonlyregarded as an extremely delicate instrument and will be degraded in operation by the pressure of extraneous-magnetic and radio frequency fields. vSome ionization chamber-types are-perhaps slightly-less costly .and -more rugged, ibutthey are 'notfdeemed sensitive to the extent required for human safety. 1 'L-It is a general purpose of the present invention to -a cost commensurate, with good business practice. f

It is, therefore. an object of the present invention 0 provide an improved device for detecting and indicating ionizing radiation having an extremelyhigh sensitivity relative toexist'ing' devices, which is light and. compact so satisfy the need for an ionizing radiation detector 'having all of the advantages of the known types of detectors at spectral region in" which the .photoconductive material 17 is most sensitive The light so produced'from a single radiation event appears as a flash or scintillation in crystals located inside the scintillationmaterial, the intensity being proportional to the energy of'the radiation.

The electroluminescent material 18" is comprised of a composition, suchas activated zinc selenide- (ZnSe), or amixture characterized by thewproperty of emitting light inthe spectral region to which the photo-conductive material 17 is most responsive when it is subjected to an electric field.

It is contemplated that an electroluminescent material or photoconductive material, capable of performing the functions of thescintillationmaterial 17, may obviate the need for thelatter. It should thus be apparent that it is notintended to limit the inventiveconcept to the particular materials selected to obtain the three separate and distinctfunctions as set forth above.

The alternating current supply'll produces an excitation at a selected voltage and a frequency whereby a maximum light output of the electroluminescent material 18 will occur in the' most sensitive spectral region of'the photoco'nductivematerial 17 with only a slight decrease "in resistance across the plates 14. For the'illustrated that it can be easily carried about by a person-engaged in I ordinary activities, which isof rugged construction, which I is insensitiveto strong'magnetic and radio frequency voltage for its operation.

embodiment, best results were obtained with an excitation of 300yolts, at 10 kilocycles.

Theindicator 12 can be any direct-reading typeof devicewhich is responsive to pulsating current in the closed series circuit, "ranging from simply a neon light. to a pulse-counter. The quencher IS- 'may be of any well 0: fieldaand ,which requires no directcurrent regulated known pawn design such as a degenerative feedback 'amplifier} a high resistance, or a combination thereof. The quencher 13 functions to change itselffrom a state The threematerials are a 9 l a of conduction to one of cut-oil when undergoing a rapid upward change in voltage. The large resistant type will serye for this purpose at low pulse or counting rates, while a degenerative feedback amplifier is desirable for 7 higher pulse or counting rates.

The operation of the device is summarized as follows.

In the operative condition of being ready to detect and ticulate or electromagnetic character, the scintillation material 16 converts the-energy to light in the spectral region at which the photoconductive material 17 is most sensitive. The light so produced substantially reduces the impedance of the-photoconductive material 17 causing thereby a substantial increase in current, above the threshold current, through the detecting head ltl in the series circuit as generated at the alternating current supply 11.. This current will cause the electroluminescent material 18 to glow and emit light in the same spectral region. Feedback of this light to the photoconductive material 17 will result in a greater current which, in turn, .gencrates more light from the electroluminescent material 18, until the whole cell is glowing andin a conducting state. The alternating current supply ll'ha'ving an output such as 300 volts, 1O kilocycles, maintains the electric field between the electrode plates 14. At 'a prescribed instant, as determined by the quencher 13, the, conduction is cut oil and the detecting head to is restored to its original nonconducting state. Obviously, the time constant of the quencher 13 determines the maximum pulse or counting rate at which the detecting'head will respond. j

It is thus apparent that a single event of ionizing radiant predetermined value; and an electrical conductor means connecting said detecting head, said alternating current supply, said indicator and said quencher in series to form a closed circuit; whereby said detecting head con-. ducts a current through saidcircuit when it is subjected to ionizing radiation. t

2. Apparatus for detecting and indicating ionizing radiation comprising, in combination: a normally nonenergy imparted to the detecting head ll) produces an avalanche of electron multiplication by the interaction of the scintillation material 16, the photoconductive material 17, and the electroluminescent material 18, until the multiplication reaches the maximum level determined by the quencher 13. Each event causes a pulse at the indicator l2, and the number of pulses per unit of time is indicative of the counting rate of ionizing radiation.

The advantages of the ionizing radiation detector and indicator of the present invention are distinct over existing methods and apparatus in both construction and functions. The device can be made in any convenient size, and provides a sensitivity of from .40 to 400 times that of heretofore existing devices. The device is also insensitive to strong magnetic and radio frequency fields, making it useful as a warning device for .X-ray coming from radar transmitters or other electronic gear.

It is understood that the materials and apparatus used and their particular arrangement 'with'rrespect to each, hereinabove disclosed, are for illustrative purposes only and are not intended to limit the scope of the; invention to these precise materials and apparatus.

Itv will be further understood that various changes of the details, materials, steps and arrangement of parts,

which have been herein described and illustrated-in orderv to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims. What is claimed is: 1. Apparatus for detecting and indicating ionizing radiation comprising, in combination: a normally nonconductive detecting head having scintillation, photoconductive, and electroluminescent materialsn disposed between a pair of conducting plates; an alternating cu rrent supply; an indicator responsive to currentfiowya.

quencher adapted to stop current flow therethrough at a conductive detecting head having the properties of scintillation, photoconduction, and electroluminescence disposed between a pair of conducting plates; an alternating current supply; an indicator responsive to current flow; a quencher adapted tostop'cu'rrent flow therethrough at a predetermined 7 value; and an electrical conductor means connecting said detecting head, said alternating current supply, said indicator and said quencher in series 'to form a closed circuit; whereby said detecting head conducts through said circuit when it is subjected to ionizing radiation.

3. Apparatus for detecting and indicating ionizing radiation comprising, in combination: a normally nonconduetive 'detecting'head having a photoconductive materialmaxirnally responsive in a prescribed spectral region of light, ascintillation material maximally generative of light in said spectral region; and an electroluminescent material maximally generative of light in said spectral region disposed between a pair of conducting plates; an alternating current supply; an' indicator responsive to current flow; a quencher adapted to stop current flow therethrough ,at a predetermined value; and an electrical con- "ductor means connecting said detecting head, said alternating current supply, said indicator and said quencher in series to form aclosed circuit; whereby said detecting head conducts a' current through said circuit when it is subjected to ionizing radiation;

4. Apparatus for detecting and indicating ionizing radiationcornprising, in combination: a norm-ally noncond-uctive detecting head having the properties of being maximally conductive in a prescribed spectral region of light, maximally generative of light in said spectral region in response to ionizing radiation, and maximally generative of light in said spectral region in response to an electric field disposed between a pair of conducting plates; an alternating current supply; an indicator responsive to current flow; a quencher adaptedto stop current flow therethrough at a predetermined value; and an electrical conductor means connecting said detecting head, said alternating current supply,

said indicator and said quencher in series to form a closed circuit; whereby said detecting head conducts a current through said circuit when it is subjected to ionizing radiation. v

5. Apparatus responsive to ionizing radiation comprising: a photoconductive material maxim-ally responsive in a prescribed spectral region-'oflight, a scintillation material maximally generative of light in said spectral region,

and ran electroluminescent material maximally generative of light in said spectral region disposed between a pair of conducting plates; whereby the impedance of said detecting head rapidly decreases when it is subjected to ionizing radiation; I 1 I 6. Apparatus responsive to ionizing radiation comprising: an outer layer scintillation material, an inner photoconductive material, and an outer layer of electroluminescent material, said outer layers being disposed between a pair of conducting plates; means applying A.C. voltage across said pair of conducting plates whereby said detecting head conducts a current therethrough when it is subjected to ionizing radiation; 7

References Cited in the file of this patent V UNITED STATESPATENTS 2,837,661 Orthuber etal. June 3, 1958 2,899,560 Nernet -I Aug, 11, 1959 2,986,635 Schultz May 30, 1961 

1. APPARATUS FOR DETECTING AND INDICATING IONIZING RADIATION COMPRISING, IN COMBINATION: A NORMALLY NONCONDUCTIVE DETECTING HEAD HAVING SCINTILLATION, PHOTOCONDUCTIVE, AND ELECTROLUMINESCENT MATERIALS DISPOSED BETWEEN A PAIR OF COINDUCTING PLATES; AN ALTERNATING CURRENT SUPPLY; AN INDICATOR RESPONSIVE TO CURRENT FLOW; A QUENCHER ADAPTED TO STOP CURRENT FLOW THERETHROUGH AT A PREDETERMINED VALUE; AND AN ELECTRICAL CONDUCTOR MEANS CONNECTING SAID DETECTING HEAD, SAID ALTERNATING CURRENT SUPPLY, SAID INDICATOR AND SAID QUENCHER IN SERIES TO FORM A CLOSED CIRCUIT; WHEREBY SAID DETECTING HEAD CONDUCTS A CURRENT THROUGH SAID CIRCUIT WHEN IT IS SUBJECTED TO IONIZING RADIATION. 